It is known that a free electron laser is a high efficiency wavelength-tunable laser and is able to emit a high-powered electromagnetic radiation and, to this effect, uses the characteristic feature of a beam of relativistic electrons to emit a coherent electromagnetic radiation when it is subjected to a static yet spatially periodic magnetic field generated by a device known as a wiggler.
Such a laser may be an amplifier and function without any optical cavity, or an oscillator in which an optical cavity is required so as to trap the radiation emitted by the beam of relativistic electrons.
Various free electron lasers are described in an article (1) by C. W. Robertson and al. and entitled "A review of free electron lasers" and published in the Physics of fluids journal, B1, January 1989.
Existing free electron lasers have the drawback of requiring beams of electrons with extremely high energy and thus expensive accelerators and thick protection devices so as to obtain electromagnetic radiations with short wavelengths.
There is also an existing free electrons laser disclosed by an article (2) by R. H. Pantell and al, Journal of the optical society of America B: optical physics, vol. 6, No. 5, May 1989, p. 1008 to 1014 and by an article (3) by M. B. Reid and al., IEEE Journal of quantum electronics, vol. 5, No. 1, Jan. 1989, p. 84 to 87, these articles to be referred to subsequently, the tuning condition of this free electrons laser being modified by introducing a gas into the wiggler of the laser.
However, a considerable modification of the tuning condition requires high gas pressure, which results in the wiggler having to be materially separated from the pipe linking the latter to the electrons accelerator associated with the laser.